Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

107
FXUS63 KLOT 011713
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1213 PM CDT Fri May 1 2026

.KEY MESSAGES...

- Frost development is expected tonight into early Saturday
  morning across many areas.

- There is a low (~15-25%) chance for thunderstorms late Sunday
  followed by a better (~30-40%) chance for thunderstorms on
  Monday.

- Outside of a brief warmup early next week, near to below
  normal temperatures are favored through next week with
  occasional chances for rain showers.

&&

.DISCUSSION...
Issued at 329 AM CDT Fri May 1 2026

A few lingering showers are still ongoing early this morning as
an upper-level shortwave trough continues to pivot through the
area. Subsidence on the backside of this wave should bring an
end to this precipitation by mid-morning, but steepening low-
level lapse rates amidst filtered diurnal heating and modest
cold air advection may pave the way for the redevelopment of
isolated showers or sprinkles in some spots this afternoon as
another shortwave approaches the area. It`s possible that a
slightly greater coverage of showers may be realized along the
lake breeze, where surface convergence will provide a localized
boost to cumulus growth, but with low-level moisture looking
somewhat limited, didn`t see a need to go with anything higher
than slight chance PoPs in the forecast grids at this time. The
combination of cloud cover and cold air advection will result
in unseasonably cool temperatures for the start of May, with
high temperatures today expected to range from only the mid 40s
to the mid 50s (coolest near Lake Michigan).

Surface high pressure will build into the region tonight,
causing winds to become light/calm. Skies should also start to
clear out as the secondary shortwave departs, and frost
development should ensue thereafter with efficient radiational
cooling allowing for air temperatures to dip into the low-mid
30s across most of the area. Have hoisted a Frost Advisory with
the expectation for widespread frost development across most of
our CWA, though there are a couple of exceptions. One of these
exceptions is our southern/southwestern counties, where
uncertainty remains regarding whether clouds will clear out in
time and allow for temperatures to fall enough to be conducive
for frost development. It is also probable that the urban heat
island effect may keep temperatures high enough to preclude
frost development within most or all of the city of Chicago and
its closest suburbs, so have kept central Cook County out of the
advisory as well, at least for now.

Dry conditions and similar to perhaps slightly milder high
temperatures are expected on Saturday before the next shortwave
trough in this northwest flow pattern reaches our area on
Sunday, bringing our next chances for precipitation. Existing
uncertainties with respect to the trajectory of the shortwave
and the timing of its arrival preclude having any PoPs higher
than 30-40% in the forecast grids at this time, with several
ensemble solutions suggesting that there are many scenarios
where most or all of our forecast area could stay dry through
Sunday night. That said, should the shortwave arrive at an
optimal time and take a favorable track that would maximize
synoptic-scale lift over northern Illinois and northwestern
Indiana, then mid-level lapse rates would become steep enough to
be supportive of a few thunderstorms in our area during the
afternoon and/or evening.

Breezy southwesterly winds are also expected to develop on
Sunday as a weakening surface low tracks into Ontario and will
help push temperatures back into the 60s across the area. These
southwesterly breezes will continue into Monday as a deeper
surface low associated with a more pronounced upper-level trough
dives southeastward from the Canadian Prairies into the
northern Great Lakes. Continued warm air advection off of these
winds will propel temperatures into the 70s south of an inbound
cold front on Monday, while also inducing an influx of better
low-level moisture that will bring an increased chance for
showers and thunderstorms to our area along and ahead of the
cold front as it scoots on through. Strengthening mid- to upper-
level flow along the southern periphery of the aforementioned
trough could support some organization to these storms, but
only modest destabilization and subpar lapse rates will be
limiting factors for how strong storms will be able to get
across our forecast area.

Aggregate troughing and northwest flow over the Great Lakes and
Midwest will then remain the theme for the synoptic upper-level
pattern for the remainder of the week and into next weekend.
This will favor the persistence of near to below normal
temperatures after Monday`s cold frontal passage and should
allow for additional periodic opportunities for rain showers as
more disturbances embedded within the mean longwave troughing
and northwesterly flow aloft dive into the region.

Ogorek

&&

.AVIATION /18Z TAFS THROUGH 00Z SUNDAY/...
Issued at 1213 PM CDT Fri May 1 2026

Key Messages:

- Easterly wind shift at the main Chicago terminals ongoing
  with lake breeze boundary.

- A few isolated to widely scattered showers and locally lower
  CIGs possible (20-30% chance) this afternoon.

- Northerly winds turn northeasterly again across northeastern
  IL and northwest IN Saturday afternoon.

Similar to yesterday at this time, a lake breeze boundary is
again in the process of moving right across ORD and MDW. Winds
at the main Chicago terminals will thus settle into an easterly
direction for the remainder of the day. Winds will then ease
this evening and may go variable for a period overnight. Wind
trends on Saturday then look to mimic those of today, with
directions settling in a north-northwesterly direction after
daybreak Saturday morning, then shifting easterly with another
lake breeze for the afternoon.

Otherwise, expect lower VFR CIGs this afternoon, along with some
isolated to widely scattered showers. The coverage of showers
this afternoon should be lower, and of shorter duration, than
those observed yesterday afternoon and evening. The best chances
(20-30%) for these showers will be in the vicinity of the lake
breeze boundary across northeastern IL and northwestern IN. To
account for this, we have opted to add a PROB30 mention for some
showers. The threat for these will wane prior to sunset this
evening.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Frost Advisory from 1 AM to 8 AM CDT Saturday for ILZ003-
     ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-
     ILZ020-ILZ023-ILZ033-ILZ103-ILZ105-ILZ106-ILZ107-ILZ108.

IN...Frost Advisory from 1 AM CDT /2 AM EDT/ to 8 AM CDT /9 AM EDT/
     Saturday for INZ001-INZ002-INZ010-INZ011-INZ019.

LM...None.

&&

$$

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